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Literature Review Article
Cone beam computed tomography and
applicability in Dentistry – literature review
Fabiana Caroline da Silva1
Ilana Sanamaika Queiroga Bezerra2
Nelson Luis Barbosa Rebellato1
Antonio Adilson Soares de Lima1
Corresponding author:
Fabiana Caroline da Silva
Rua Augusto Klimmek, n. 508 – Centro
CEP 89280-301 – São Bento do Sul – SC – Brasil
E-mail: [email protected]
1
2
Department of Stomatology, School of Dentistry, Federal University of Paraná – Curitiba – PR – Brazil.
Department of Oral Diagnosis, State University of Campinas – Piracicaba – SP – Brazil.
Received for publication: July 30, 2012. Accepted for publication: January 29, 2013.
Keywords: X-ray
computed tomography;
radiology; imaging
diagnostic.
Abstract
Introduction: An appropriate treatment planing is essential for
successful rehabilitation in Dentistry. The cone beam computed
tomography (CBCT) represents a valuable resource in dental practice
because it allows the establishment of a precise treatment plan by
means of diagnostic imaging. Objective: To review the literature on
CBCT. The history of development of this technique, its benefits and
its applicability in different areas in Dentistry will be considered.
Literature review: The CBCT offers advantages over the quality and
quantity of anatomical data and promises less distortion of the image
with low doses of radiation. It has been established as a valuable
technique in the dental specialties. Conclusion: The use of CBCT as
a diagnostic method must have precise and appropriate indication to
provide adequate cost-benefit effectiveness in the patient’s treatment.
Introduction
The adequate treatment planing is indispensable
for the rehabilitative success in Dentistry. The
evaluation of surrounding dental structures through
imaging resources is one of the prerequisites and
it has been used by several dental specialties.
The multiplanar ability of generating images in
axial, coronal and sagittal planes are provided by
computed tomography (CT), magnetic resonance,
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ultrasound and cone beam computed tomography
(CBCT). These semiotics resources enable the
professional to recreate the anatomical forms
with simple functions increasing the efficacy in
diagnosing the clinical cases [2, 12, 20].
Literature review and Discussion
CT development dates from the last of 1960s.
However, it was patented by Hounsfield, and
British engineer in the year of 1973. The invention
promoted an immediate and profound impact in
the imaging diagnosis granting him the Nobel
Prize in Medicine, in 1979 [21]. From that moment
on, the tridimensional imaging provides dramatic
changes in medical and surgical practice. With the
use of a new technology through the years, the
professionals were able to apply this technology
for the benefit of the patients [24]. The first
generation of CT devices obtained data only in the
axial plane of the patient, slice by slice, through a
thin beam of x-rays penetrating a single matrix of
detectors. In the last three decades, considerable
advancements in technology allowed scanning in
different planes; currently the scanners have a linear
matrix of multiple detectors that obtain several cuts
simultaneously, that are “piled up” and reformatted
to obtain tridimensional images [21].
CBCT was initially developed for the use
in angiography [24, 27]. It is a technique of
tridimensional image acquisition developed in
the last decades of the past century based on the
application of the x-ray beams as conical-shaped
centered in image detectors. At the ending, the
morphology of the region is reconstructed in 3D
by a data set converter by using a modification
of the original cone beam algorithm developed by
Feldkamp et al. in 1984 [30]. CBCT was previously
used by radiotherapy and it has been applied in
nuclear, war and spatial industry, in addition to
medicine [6]. This technology was introduced in
dentomaxillofacial imaging between the years of
1998 and 1999 [8]. A source of conical-shaped
ionizing radiation is directed through the middle
of the area of interest towards to an area of xray detection at the opposite side. The radiation
source and the detector rotate around a fixed
fulcrum inside the center of the area of interest.
During the rotation, from 150 to 600 projections
of planar sequential images of the field of vision
are completely or partially acquired and, following,
they are piled up to obtain a 3D representation.
This procedure is different from traditional CT,
because it uses a fan-shaped x-ray beam at a helical
progression to acquire individual slices by image.
CBCT comprises the entire field of view (FOV) and,
at only one rotation sequence, it is able to acquire
sufficient data for reconstruction [27]. The quality
images and the resolution capability of CBCT are
influenced by some variables including the device
type, FOV, voxel size, current and tube voltage and
other technical factors [15].
The first CVCT devices were commercially
available in 2000 [20]. In USA, the devices started
to be used in 2001 [14]. Since that moment, the
researches show the use of this technology in
Dentistry, so that the scanners have been constantly
improved for use in dental offices [20].
CBCT systems commercially available are
categorized according to the detector technology
and design: a combination of devices coupled to
an image intensifier tube or flat screen detector.
This latter exhibits less influence of artifacts which
are defined as distortions in images caused by
metals, such as those within either restorations
or orthodontic brackets [13].
There are four important 3D views: axial,
transversal or sagittal, panoramic or coronal
a nd the 3D reconstructions. The pa nora mic
image reconstructed from the data set of CBCT
differs substantially from that produced in the
conventional panoramic radiograph and it can be
viewed through software for the evaluation of the
most comprehensive aspects of the arch [11]. CBCT
enables the planing in virtual 3D softwares [6,
13]. The literature has shown that these softwares
show the morphology with a clinically significant
way and that the primary reconstruction of the
data is completed parallely to the occlusal plane,
which becomes the landmark. Other authors still
affirmed that the reconstructions can also occur
at the curve planes and oblique vision [14].
The position of the patient in the CBCT shot
for the bucomaxillofacial region is either sitting
or standing instead of only supine [6, 13, 27].
The device which demands that the patient lays
at dorsal decubitus, occupies a larger area of
surface or physical space and it cannot be used
for physical impaired patients; also the units where
the patient stays standing cannot be adjusted for
an adequate height to fit a wheelchair; so devices
where the patients stays sitting are more viable and
comfortable. However, the head support devices more
important than the patient orientation [27].
CB C T i s a l re ady k now n a s mu lt i- sl ice
tomography and it is a diagnosis record that
currently promises less image distortion without
superimposed structures [25]. The technological
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advancements in 3D images offer significant
advantages regarding to the quality and quantity
of the anatomical data because of the accuracy and
proximity with the reality [16].
This technique decreases the “noise”, which
can be interpreted as image variations from
electronic, artifact or purely stochastic interferences,
interposing in the quality and detection of important
structures, fact very evident in 2D image [10].
CBCT uses a radiation dose significantly smaller
than conventional CT [1, 4, 6, 8, 9, 11, 12, 14, 19,
21, 24, 30, 31]. This technique enables a reduction
in the radiation absorbed by the patient because
it utilizes a single 360º rotation and a cone beam,
while spiral CT comprises several rotations and a
fan beam [6, 13]. The radiation dose in CBCT is
about 40% smaller than CT, but still 3 to 7 times
greater than that of the panoramic radiographic
examinations. This fact reinforces that when a 3D
image is required, CBCT should be the method of
choice [28].
The authors have emphasized the resolutive
spatial superiority of CBCT in relation to CT [31].
The voxel size in CBCT can be up to 0.1 mm.
This fact enables the establishment of a resolution
greater than CT which reaches only to 0.5 mm [6,
13]. The disadvantage of CT is its high cost and the
device size, generally inside hospital environments
[6, 21].
CBCT introduction creates new diagnosis
resources in Dentistry and it has been established
as a valuable technique in bucomaxillofacial, oral
surgery and orthodontics specialties [2, 4, 8,
15]. This technology becomes and indispensable
diagnosis tool to be applied in different clinical
applications, including: evaluation of the receptor
site of osseointegrated implants and bone defects;
bone graft procedures; evaluation of impacted teeth;
orthodontic and endodontic planing; investigation
of t he TMJ disorders; procedu res of si nus
augmentations and orthognathic surgeries [11].
A compa rat ive st udy reve a led t h at t he
identification of cephalometric points used in
the orthodontic planing was significantly more
accurate with CBCT than with conventional lateral
cephalogram [18]. The volume of the airways and
respiratory function are highly relevant for this
specialty, because different types of malocclusion
and nasal obstruction are important etiologic
factors for dentofacial anomalies. Obstructive sleep
apnea exhibits craniofacial differences such as the
size and position of the mandible, enlargement of
the posterior air space and tongue and soft palate
size. The use of CBCT to evaluate the airways
can provide clinically useful information for the
orthodontic treatment [12].
A st udy compa r i n g t he d i rect orona sa l
anthropometry with 3D through surface molds
created from CBCT in cadavers showed t he
superiority of this latter technique. The data set
obtained by CBCT was accurate and exhibited an
excellent reproducibility compared with the manual
method. Additionally, the second method was faster
in collecting the data, less invasive and enabled the
obtained of a 3D file of the facial morphology of the
individual [9].
A study comparing the vertical angulation of
all canines of 29 patients at the final phase of the
orthodontic treatment concluded that the panoramic
radiograph exhibited distortions in the images. This
limits its value as a method for assessment of the
tooth angulation and mesiodistal angles, which
were always greater than those measured through
CBCT [25].
The images of the cysts and tumors in the
maxillofacial area can provide the bucomaxillofacial
surgeon the information necessary for the surgery
planing; with an accurate volumetric analysis, the
CBCT scanning can predict the need and volume of a
potential graft for reconstruction. Although the magnetic
resonance examination is considered as the gold
standard in the evaluation of the temporomandibular
disorders, the condition of the bone components of the
joint is offered with excellence by CBCT [24].
CBCT has been considered as an imaging
modality very adequate for the assessment of the
craniofacial area. It provides clear and accurate
images of the structures, and therefore, it is extremely
useful for the evaluation of the bone component.
The transversal images can be used for obtaining
more information on the appearance, location and
path of the root canals and their relationship with
other mandibular anatomical structures, including
the tooth apexes [3].
Some authors considered CBCT as fundamental
to evaluate the position and path of the inferior
a lveola r ca na l, ma i n ly i n cases of su rg ica l
intervention. This avoids nervous damages such as
neuropraxia, axonotmesis and neurotmesis caused
by either dilacerations, compression or stretching
of the inferior alveolar nerve [7].
The literature suggests that CBCT is more
sensible than conventional radiographs regarding to
the location of included canines and root resorptions
of the surrounding teeth. In 2D projections, a wrong
interpretation can occur because of errors caused by
projection distortions and blurred images [1]. It is clear
the value of the CBCT in the planing of implants,
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surgical evaluation of the diseases, temporomandibular
conditions and pre- and post-evaluations of the
craniofacial structures [8, 11, 18].
Due to the increase of the requirement for
rehabilitation of edentulous mandibles through
osseointegrated implants the knowledge of the
variations in dimensions and morphology of the
endosseous arteries is very important. A study
evaluating the distribution of endosseous canals
in mandible through CBCT found these structures
in 85% of t he pat ients. This fact reinforces
t he indicat ion of t his technique in t he preoperative diagnosis, reducing the risk of surgical
complications [26].
The literature describes the rich anatomical
details provided and the importance of this resource
in the surgical planing in Implantolog y. With
the advent of CBCT, a valorization of important
anatomical structures such as the ma xillary
sinuses, lingual and mental foramens, the level of
bone resorption in edentulous areas and vascular
and surrounding nervous bundles/branches [2].
An in vivo study revealed the success in the preoperative orientation through CBCT in maxillary
sinus augmentation and implants installation
without transalveolar flap [8].
The traditional radiographs provide adequate
i n format ion on t he sites for i nst a l lat ion of
osseointegrated implants. However, the limited size
of the film, the image distortion, the enlargement
and the 2D view generates data and measurement
inaccuracy. Thus these factors limit their use [6, 22].
Studies confirmed the existence of the enlargement
rate in panoramic radiographs and suggested the
CBCT utilization for the pre-operative evaluation in
Implantology. CBCT eliminates this limitation and
increases the examination accuracy [18, 31].
CBCT avoids the potential complications such
as paresthesias, coming from the cortical bone
perforation, reaching the inferior alveolar nerve,
mental foramen and incisive canal; or seven the
bad positioning of the implant inside the bone
without the adequate surrounding bone volume,
compromising its stability. The cross-sectional image
is excellent for defining a cut in which the height
and width of the bone can be accurately assessed.
The simulated implants can be positioned into the
ideal place for posterior rehabilitation [11].
In Endodont ics, li mited CBCT sca nners
capture small volumes that may include only two
or three individual teeth. The images obtained
eliminate the superimposition of the anatomical
structures, such as the roots of the posterior teeth
and their periapical tissues. These structures can
be visualized separately at the three orthogonal
planes without the superposition of the zygomatic
bone, alveolar bone and surrounding structures.
Additionally, the thickness of the cortical plate,
the pattern of the bone marrow, presence of
fenestrations, inclination and morphology of tooth
roots, as well as the number of divergent and
convergent canals can be detected. The presence
of not identified canals, consequently not treated,
it is easily identified at the axial cuts. They cannot
be readily seen in the periapical radiographs, even
those obtained at different angles [21].
The correct dia g nosis of t he a natomica l
variations is important for the success of the
endodontic treatment. An in vitro study analyzing
the morphology of the root canals in human teeth
concluded that the tridimensional image provided
by CBCT is a great advancement as an auxiliary
method to establish the endodontic diagnosis [5].
A comparative in vitro study revealed that CBCT
accuracy in detecting periapical lesions chemically
induced was higher than that from conventional and
digital radiographic images. This result is explained
by the fact that in an image in layer, the difference
between the lesion and its surrounding bone is
greater resulting in a better contrast than that of 2D
images [29]. Other in vivo study demonstrated that
25.9% of the periapical lesions in the pre-operative
period of the apical surgery diagnosed in the CBCT
examinations had not been detected by periapical
radiographs. These findings once more reinforce
the resolutive superiority of CBCT [4].
The authors emphasized that among the
disadvantages of the panoramic radiograph are:
projection of anatomic structures and differences
in the mandibular morphology (like the mylohyoid
nerve impression on the mesial surface of the
mandible). Thus, they decided to investigate the
presence of bifid mandibular canals in a sample
of 84 individuals. The results demonstrated that
the presence of these canals was detected with
statistically significant difference when CBCT and
panoramic radiographic images were compared.
This suggests that the cone-beam system improves
the diagnosis and prognosis of the clinical and
surgical procedures at the retromolar region and
mandibular body [17].
The disadvantages associated with CBCT
includes the radiation dispersion, the limited
dynamics reaching, the minimum detail of the soft
tissue, and the presence of the artifacts caused by
some dental materials and implants [15].
Some authors believe that the ionizing radiation
is the key parameter limiting the use of this
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examination and they recommend that at any
phase of the treatment one must follow the ALARA
principle. ALARA is the acronym for “as low as
reasonably achievable”. It is a safe principle for
radiation safe aiming to the decreasing of the doses
to patients and workers as well as the discard of
remnants of radioactive materials employing all
reasonable methods [25].
Conclusion
CBCT is an excellent diagnosis tool, offering
significant advantages regarding to the quality and
quantity of anatomic information. When 3D image
is necessary, CBCT should be the method of choice
always justified by an accurate indication. This will
provide an adequate cost/benefit ratio both for the
treatment and patient.
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